Electric tachometer



1956 w. w. HASTINGS 2,774,939

ELECTRIC TACHOMETEIR Filed May 18, 1955 IIIIIIIIIIIII'IiiIIIII Vlijiii DVARREA I tZ f S T INGS HG-Z ATTORNEY United States Patent ELECTRICTACHOIVIETER Warren Walker Hastings, Rochester, N. Y., assignor toRochester Manufacturing Company, Inc., Rochester, N. Y., a corporationof New York Application May 18, 1955, Serial No. 509,305

Claims. (Cl. 32470) The present invention relates to tachometers, andmore particularly to tachometers for use on automotive vehicles.

One object of the invention is to provide a tachometer, the actuatingmechanism of which, at least, can be made part of already-existingequipment of an automotive vehicle.

Another object of the invention is to provide a tachometer havingactuating mechanism that can be incorporated in the distributor of anautomotive vehicle so that it will be compact, and will not require anyadditional drive or mounting in the vehicle.

Another object of the invention is to provide a tachometer that will besimple in construction, yet accurate.

Other objects of the invention will be apparent hereinafter from thespecification and from the rec-ital of the appended claims.

In the drawing:

Fig. 1 is an axial section through a conventional automotive distributorshowing the actuating mechanism of my tachometer mounted therein, thebreaker points, cam, condenser, terminals, spring, and otherconventional parts of the distributor being omitted for the purpose ofclearness in illustration of the invention;

Fig. 2 is a plan view of the rotor of the distributor, showing themounting for the resistor and rocker spring which actuate my tachometer;

Fig. 3 is a section on the line 3--3 of Fig. 2, looking in the directionof the arrows and particularly showing the shape of the contact portionof the rocker spring;

Fig. 4 is a section on the line 4-4 of Fig. 2 looking in the directionof the arrows;

Fig. 5 is a plan section of the modified breaker cover used in thedistributor;

Fig. 6 is a section on the line 66 of Fig. 2 looking in the direction ofthe arrows, and on a somewhat enlarged scale;

Fig. 7 is a section on the line 7-7 of Fig. 2, looking in the directionof the arrows, and also on an enlarged scale; and

Fig. 8 is a wiring diagram, showing how the tachometer is wired.

Referring now to the drawings by numerals of reference, 10 denotes thehousing and 11 the cap of a conventional automotive distributor. The capis removably secured to the distributor housing in conventional mannerby a plurality of spring clips 12 which snap over the cap and which arepivotally secured at their lower ends to straps 13 that are secured byscrews or rivets 14 to the housing.

The distributor shaft is denoted at 16. It is journaled in the housingin conventional manner on a bushing 17. The rotor 20 is fixedly securedto the upper end of the distributor shaft. It carries the conventionalcurrent spring 21 which conducts in conventional manner the high voltagecurrent from the secondary of the ignition coil to the sockets 23 whichreceive the jack-connections for the spark plugs of the vehicle.

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All this is conventional construction. The new feature is the use of therotor for operating a tachometer.

This tachometer-actuating mechanism includes a wire wound, or carbon,resistor 25 and a rocker spring 26 which cooperates therewith. Theresistor is pivotally mounted on a shaft 28 (Figs. 6 and 7) which ishollowed at its lower end, as denoted at 29, and which has its lower endspun over to secure it in the rotor. The resistor is pivotally mountedon the bearing portions 30 and 31 of the shaft by means of a bushing 33.The bearing portions 30 and 31 are eccentric of the axis of the shaft.The pivotal mounting of the resistor permits the resistor to swing aboutits pivotal axis under centrifugal force as the rotor revolves in theoperation of the automotive vehicle.

The resistor is constrained to remain in a horizontal plane during itsswinging movement by a guide shaft 34 which has a pressed fit in a holein the core of the resistor, and which engages in an elongate slot 35 ina bracket 36 which is riveted or otherwise secured to the rotor body.The guide shaft 34 has a shoulder portion 38 which seats against theresistor core.

The rocker spring 26 is a single piece of flexible strip materialsecured at one end in a kerf 39 in a retainer 40. The kerf 39 is formedin a cylindrical portion 41 of the retainer that is eccentric of theaxis of the retainer so that by rotation of the retainer the tension ofthe spring can be adjusted. The retainer may be fastened in the rotor bymaking it hollow at its lower end, and spinning its lower end over, asdenoted at 43. The spring 26 is positioned so that it has oscillatingcontact at only one point along its length, at a time, with theresistor; and as the resistor pivots on shaft 28, this point oflengthwise contact changes. The resistor, in effect, has rollingengagement with the spring. The spring is made fiat in transversesection for the major portion of its length, as shown in Fig. 4, but ismade convex in transverse section, as denoted in Fig. 3, for thatportion of its length which is in contact with the resistor, so that thecontact between the spring and the resistor will be limited to pointcontact, thereby giving the greatest accuracy in reading of thetachometer.

Mounted on the breaker cover 50 of the distributor are two concentric,electrically-conducting, contact rings 51 and 52. The spring retainer 40is connected by a wire 55 to a brush 57 which rides on the inner ring51. One end of the resistor is connected to shaft 28 which in turn isconnected by wire 56 to a brush 58 which rides on outer contact ring 52.The inner contact ring 51 is grounded to the distributor housing by anelectrical wire or conductor 53 which is secured in conductingengagement with strap 13 by the head of screw 14. The outer contact ring52 is connected by a line 54 in series with an indicating meter, and thebattery of the vehicle. The indicating meter which may be a conventionalgalvanometer, is denoted at G in Fig. 8. The battery is denoted at B inthis figure. One pole of the battery is grounded to complete theindicator circuit.

The resistor may be of standard construction. It may be a carbonresistor or it may comprise a multiplicity of turns of fine Wire woundvery close together. In the latter case, the coil has the insulationremoved from one side as by means of a coarse emery cloth, and is coatedwith an insulating varnish except where the insulation is removed. Ineither case, as the resistor pivots under action of centrifugal force,the contact spring engages and rocks along the resistor. In the case ofthe wire wound resistor, of course, the contact'spring rocks over theportion of the resistor coil from which the insulation has been removed.The spring contact arm has an osculating, rolling, contact with theresistor. It is held spring pressed into engagement with the resistor byits own inherent resiliency.

The rotor is driven in time with the motor of the automotive vehicle.The faster the rotor rotates, the more the resistor is thrown outwardlyabout its pivot by centrifugal force, thereby rolling along the springcontact member. The speed of rotation of the rotor determines themovernent of the resistor about its pivot, thereby determining the pointof contact of the spring contactor with the resistor. This determinesthe amount of resistance in the circuit to the galvanomcter. The needleof the galvanometer thereby registers the speed of rotation of the rotorof the distributor, namely, the speed of the engine.

The spring contact member has almost frictionless action resulting invery little lag; and it permits using great pressure between theresistor and:the contactor. Because there is no intermediate linkage theactionisvery smooth and trouble free. In addition, the transmitter orsender is simple, rugged, and inexpensive to build since it contains sofew parts. It is suitable for truck-tractor installations. It can becalibrated by rotation of the shaft 28 about its axis. Aftercalibration, shaft 28 is fixed in the factory against rotation.

While the invention has been described in connection with a specificembodiment thereof, it will be understood that it is capable of furthermodification, and this application is intended to cover any variations,uses, oradaptations of the invention following, in general, theprinciples of the invention and including such departures from thepresent disclosure as come within known or customary practice in the artto which the invention pertains, and as fall within the scope of theinvention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. A tachometer comprising a rotary member, a wirewound resistorcomprising a core and a coil of wire wound about the axis of said core,a shaft mounted in said rotary member and having an eccentric bearingportion offset from its axis, and perpendicular to the axis of said coreand on which said core is mounted to pivot about an axis parallel to theaxis of said rotary member under centrifugal force as said rotary memberrotates, and an electrically-conducting leaf spring having rollingcontact with said resistor as said resistor pivots, and means connectingsaid spring and one end of said coil electrically in circuit to actuatean indicator, said shaft being rotatably adjust able to calibrate thetachometer.

2. A tachometer comprising a rotary member, a resistor pivotally mountedon said rotary member to swing about an axis parallel to the axis ofsaid rotary member and perpendicularto the axis of resistor undercentrifugal force as said rotary member rotates, and anelectricallyconducting leaf spring having rolling contact with saidresistor as said resistor pivots, said leaf spring having a contactingportion which is of convex profile to have point contact with saidresistor.

3. A tachometer comprising a rotary member, a resistor pivotally mountedon said rotary member to swing about an axis parallel to the axis ofsaid rotary member and perpendicular to the axis of resistorundercentrifugal force as said rotary member rotates, and anelectricallyconducting leaf spring having rolling contact with saidresistor as said resistor pivots, said leaf spring having a contactingportion which is of convex profile to have point contact with saidresistor, and means for adjusting the pressure of contact of said springwith the resistor.

4. A tachometer comprising a rotary member, a resistor pivotally mountedon said rotary member to swing about an axis parallel to the axis ofsaid rotary member and perpendicular to the axis of said resistor undercentrifugal force as said rotary memberrotates, a post secured in saidrotary member to extend parallel to the axis of said rotary member, andan electrically-conducting leaf spring secured at one end to said postand having rolling contact along its free portion with said resistor assaid resistor pivots, said post being rotatably adjustable to vary thepressure of contact of said spring with said resistor, and means forconnecting said spring and one end of said resistor electrically incircuit to actuate an indicator.

5. The combination with the distributor of an automotive vehicle, havinga housing, a rotor rotatably mounted in said housing and driven in timewith the engine of the vehicle, and a pair of conductor rings secured insaid housing coaxial with said rotor, of a tachometer, said tachometercomprising a resistor pivotally mounted on said rotor for pivotalmovement under centrifugal force about an axis parallel to the axis ofsaid rotor as said rotor rotates, a spring contact member also mountedon said rotor and having resilient rolling contact with said resistor assaid resistor pivots, a brush engaging one conductor ring andelectrically connected with said spring contact member, and a secondbrush engaging the other conductor ring and electrically connected withone end of said resistor, and means for connecting the two conductorrings in series circuit with an electrically operated indicating meterand with a source of electrical power.

References Cited in the file of this patent UNITED STATES PATENTS

